Automated Teller Machines (ATMs) allow bank customers (“users”) to withdraw money, deposit money, and perform other transactions. Many ATMs are connected to interbank networks, enabling users to withdraw and deposit money from machines not belonging to the bank where they have their accounts or in the countries where their accounts are held. ATMs may rely on authorization of a financial transaction by a card issuer or other authorizing institution on a communications network.
ATMs can connect to a remote server device—sometimes referred to as a ATM “host” or “controller”—using various types of network links, including virtual private networks (VPNs) over high-speed internet connections, leased lines, or plain old telephone service (POTS) lines. Most (or all) of an ATM's functionality may be unavailable when the network link is severed or degraded.